U.S. patent application number 10/864582 was filed with the patent office on 2005-01-20 for method of forming ion transport membrane composite structure.
Invention is credited to Chen, Hancun, Chen, Jack C., Kubasiewicz, Paul James.
Application Number | 20050013933 10/864582 |
Document ID | / |
Family ID | 34272459 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050013933 |
Kind Code |
A1 |
Chen, Hancun ; et
al. |
January 20, 2005 |
Method of forming ion transport membrane composite structure
Abstract
A method of forming a composite structure for an ion transport
membrane in which a filler substance is applied to one surface of a
porous support layer in order to plug pores and prevent coated ion
conducting material from penetrating the pores to reduce the amount
of gas diffusion. Prior to coating of the surface with layers that
may be oxygen ion conducting layers, excess filler substance is
removed. After the coating of the one surface, the filler substance
is removed from pores.
Inventors: |
Chen, Hancun;
(Williamsville, NY) ; Chen, Jack C.; (Getzville,
NY) ; Kubasiewicz, Paul James; (East Amherst,
NY) |
Correspondence
Address: |
PRAXAIR, INC.
LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
34272459 |
Appl. No.: |
10/864582 |
Filed: |
June 10, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60485738 |
Jul 10, 2003 |
|
|
|
Current U.S.
Class: |
427/181 ;
427/446 |
Current CPC
Class: |
B01D 69/12 20130101;
C01B 2203/0405 20130101; B01D 69/105 20130101; B01D 71/024
20130101; C01B 3/503 20130101; C01B 2203/0475 20130101 |
Class at
Publication: |
427/181 ;
427/446 |
International
Class: |
B05D 003/04 |
Goverment Interests
[0002] This invention was made with United States Government
support under Cooperative Agreement number DE-FC26-01NT41096
awarded by the U.S. Department of Energy, National Energy
Technology Laboratory. The United States Government has certain
rights in this invention.
Claims
We claim:
1. A method of forming a composite structure for an ion transport
membrane comprising: applying a filler substance to one surface of
a porous support layer having pores such that said filler substance
enters said pores; removing excess amounts of said filler substance
from said one surface of said porous support layer; forming at
least one layer of material on said one surface of said porous
support layer with said filler substance in place, within the
pores; and removing said filler substance from said pores after
said at least one layer of material is formed on said one
surface.
2. The method of claim 1, wherein: said pores have an average
diameter of between about 0.1 and about 500 microns; and said
filler material comprises a finely divided power having an average
particle size less than that of said average diameter of said
pores; and said filler material is applied to said one surface
under pressure.
3. The method of claim 2, wherein: said filler material comprises
starch, graphite, a polymeric substance or mixtures thereof; and
said filler material is removed by heating.
4. The method of claim 2, wherein said particle size of said filler
material is between about 10 percent and about 20 percent of said
average pore size.
5. The method of claim 1, wherein: said filler material is a
substance that will dissolve in a solvent; and said filler material
is removed by dissolving said filler material by applying a solvent
to said one surface.
6. The method of claim 5, wherein said filler material comprises a
liquid which upon curing hardens into a solid and after applying
said filler material to said surface, said liquid is cured.
7. The method of claim 6 wherein said filler material is a mixture
of said liquid and solid particles.
8. The method of claim 1 or claim 2 or claim 5 or claim 6 or claim
7, wherein said at least one layer of material is applied by
thermally spraying, isopressing, or as a slurry.
9. The method of claim 8, wherein said porous support layer is
fabricated from metal and said pores are non-interconnected.
10. The method of claim 8, wherein said porous support layer is
fabricated from a ceramic and said pores are interconnected.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. Provisional Patent
Application Ser. No. 60/485,738 which is hereby incorporated by
reference as if fully set forth herein.
FIELD OF THE INVENTION
[0003] The present invention relates to a method of forming a
composite structure for an ion transport membrane in which pores of
a porous support layer are filled with a filler substance prior to
forming one or more layers of material on the porous support layer
to prevent the layers of material from clogging the pores of the
support layer.
BACKGROUND OF THE INVENTION
[0004] Ceramic membranes have found increasing application in
chemical industries for gas separation and purification. They have
the potential of replacing more traditional unit operations such as
distillation, evaporation and crystallization. Ion transport
membranes can be used to separate oxygen or hydrogen from various
feed mixtures. They are formed of ceramics that are capable of
conducting oxygen ions or protons at elevated temperature. In case
of oxygen ion transport membranes, oxygen ionizes at one surface of
the membrane known as a cathode side. The oxygen ions are
transported through the membrane to an opposite anode side. At the
anode side, the oxygen ions recombine to form elemental oxygen. In
recombining, the oxygen ions loose electrons which are used in
ionizing oxygen at the cathode side. A typical class of ceramics
that are used in forming such membranes are perovskite
materials.
[0005] The oxygen flux across the ion transport membrane is
inversely proportional to the thickness of the membrane. Thus, the
thinner the membrane, the higher the flux. However, since the
membrane is formed of a brittle ceramic, the membrane must be
supported on a porous support. The porous support can be fabricated
as the same material as the ion transport membrane or can be
fabricated from a different material or even an inert material that
does not function in the separation itself. In this regard, the
shape of the membrane can be either tubular or that of a flat
sheet. A problem in fabricating such membranes is that when layers
are applied on to the porous support layer, the pores can become
clogged with the material being deposited. As a result, the
diffusion resistance of the porous support will increase and the
performance of the membrane will consequently decrease.
[0006] A similar type of problem has occurred with respect to
turbine blade coating. Coatings are applied to turbine blades to
provide enhanced resistance to oxidation, corrosion, erosion and
other types of environmental degradation. Turbine blades are air
cooled and have air passages for passage of air to cool the turbine
blade. In order to prevent the air passages from becoming plugged
during coating, in U.S. Pat. No. 4,743,462, a fugitive plug is
placed in the opening of the cooling passage. In U.S. Pat. No.
6,365,013, a fluid is directed out of the cooling passage for such
purposes. It is to be noted that in case of composite ceramic
membranes, the pores are from 1 to 10 microns and therefore cannot
be fitted with fugitive plugs. Additionally, passing a fluid
through a porous supporting structure would disrupt the coating
process.
[0007] As will be discussed, the present invention provides a
method of forming a composite structure for an ion transport
membrane in which the support layer is treated to prevent seepage
of coating materials into pores located in the support layer.
SUMMARY OF THE INVENTION
[0008] The present invention provides a method of forming a
composite structure for an ion transport membrane. In accordance
with the method, a filler substance is applied to one surface of a
porous support layer having pores such that the filler substance
enters the pores. Excess amounts of the filler substance are
removed from the one surface of the porous support layer so that
the one surface is exposed with the filler substance plugging the
pores. At least one layer of material is formed on the one surface
of the porous support layer with the filler substance in place,
within the pores. The filler substance is removed from the pores
after the at least one layer of material is formed on the one
surface.
[0009] Preferably, the pores can have an average diameter of
between about 0.1 and about 500 microns. The filler material can
comprise a finally divided powder having an average particle size
less than that of the average diameter of the pores. The filler
material is applied to the one surface under pressure. The filler
material can be starch, graphite, a polymeric substance or mixtures
thereof. The particle size of the filler material can be between
about 10 percent and about 20 percent of the average pore size.
[0010] The filler material, alternatively can be a substance that
will dissolve in the solvent. The filler material is removed by
dissolving the filler material by applying a solvent to the one
surface. The filler material can comprise a liquid which upon
curing hardens into a solid. After applying the filler material to
the one surface, the liquid can be cured into the solid. The filler
material can be a mixture of the liquid and solid particles.
[0011] In any embodiment of the present invention the at least one
layer of material can be applied by thermally spraying, isopressing
or as a slurry, or other appropriate coating processes. The
non-porous support layer can be fabricated from a metal and the
pores can be non-interconnected, that is the pores do not
communicate with one another. Preferably, the pores can be all
substantially parallel. The pore support layer, on the other hand,
can be fabricated from a ceramic in which the pores are
interconnected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] While the specification concludes with claims distinctly
pointing out the subject matter that Applicants regard as their
invention, it is believed that the invention would be better
understood when taken in connection with the accompanying drawings
in which:
[0013] FIG. 1 is a sectional view of a support layer coated with a
filler substance in accordance with the method of the present
invention;
[0014] FIG. 2 is a fragmentary, sectional view of the support layer
of FIG. 1 with the filler substance removed from the surface;
[0015] FIG. 3 is a sectional view of the porous support layer of
FIG. 1 in which a porous layer having a network of interconnected
pores is applied to the surface of the support layer and a dense
layer of material is applied to the porous layer; and
[0016] FIG. 4 is a sectional view of a composite structure that has
been prepared in accordance with the present invention.
DETAILED DESCRIPTION
[0017] The present invention provides a method of forming a
composite structure for an ion transport membrane. In this regard,
the term "composite structure" as used herein and in the claims
means a support layer that may or may not be ion conducting that
supports at least a dense layer, that is a layer that is gas tight
and ion conducting. The dense layer can be applied directly to the
support layer or to one or more porous layers applied to the
support layer that again may or may not be ion conducting.
[0018] With reference to FIG. 1, the support layer 10 is porous and
provides a plurality of pores 12 for passage of oxygen to be
separated by a membrane that will hereinafter be applied. In the
illustration support layer 10 is a metallic support layer. Pores 12
are cylinders to provide minimum resistance to gas diffusion as
compared with porous supports that provide interconnective porous
networks. Pores 12 are formed by drilling or by electron beam
machining. In order to provide maximum mechanical strength while
maintaining optimal gas permeability, pores 12 have a diameter in a
range of between 0.1 and about 500 microns and a porosity of
between about 5 percent and about 50 percent.
[0019] As may be appreciated, if a dense layer were applied
directly to support layer 10, pores 12 would in part become clogged
with the dense layer material so as not to have the advantage of
providing minimum gaseous diffusion resistance. In order to avoid
this, filler substance 14 is applied to one surface 16 of porous
support layer 10 such that filler substance 14 enters pores 12.
[0020] The filler substance can be a finely divided powder of
graphite, starch, cellulose, sawdust, or a polymer that is applied
to the channels under a pressure of between about 10 and about 150
MPa to form solid plugs. Particle size is preferably in a range
from between about 2 and about 100 microns depending upon the
diameter of pores 14. Particle size of filler substance 14 is
preferably between about 10 percent and about 20 percent of the
diameter of pores 12.
[0021] Prior to pressing a particulate filler substance 14 in
place, porous support layer 10 can be vibrated to facilitate the
filling of pores 12.
[0022] Filler substance 14 can also be a liquid substance such as
an epoxy or glue which would be applied over surface 16. Such
liquid substance would penetrate into pores 14 by force of gravity.
As may be appreciated, if the viscosity of the liquid substance is
too low, the liquid substance will penetrate pores 12 without
filling pores 12. On the other hand, if the viscosity is too high
the liquid substance will not easily penetrate pores 12. The liquid
substance can be cured by for instance loading the coated porous
support layer 10 into an oven heated at between about 100.degree.
C. for anywhere from between about 5 to and about 50 minutes until
solid plugs are formed.
[0023] Filler substance 14 can additionally be of a particulate and
liquid substance. Such a mixture is advantageous for a very large
pores 14. Such a mixture might be applied as a paste.
[0024] Since surface 16 is to be coated with either a dense layer
or a porous layer excess amounts of filler substance 14 are removed
from surface 16 of porous support layer so that surface 16 is
exposed and filler substance 14 plugs pores 12. Removal can be
accomplished by such means as sandblasting.
[0025] Turning to FIG. 3 surface 16 is coated with a porous layer
18 and a dense layer 20 applied to porous layer 18. For instance,
layers 18 and 20 could be applied by thermal spray, isopressing or
by a slurry/coadial deposition, or by other appropriate coating
processes. Dense layer 20 conducts oxygen ions and as a gas tight.
Porous layer 18 may or may not be ion conducting and in the
illustration consists of an interconnected network of pores 22,
that is pores that intersect one another. However, it could have
non-interconnected pores, such as pores 12 within support layer
10.
[0026] With reference to FIG. 4, filler substance 14 has been
removed. In case of a particulate filler substance, filler
substance 14 can be removed by placing support layer 12 coated with
porous and dense layers 18 and 20 in an oven heated to a
temperature of between about 600.degree. C. and about 900.degree.
C. If this filler substance 14 were an epoxy or glue or other
liquid substance, removal could be accomplished by a solvent. For
instance, glues generally can be removed by acetone. The final
result is a composite structure in which pores 12 are not filled
with filler substance 14.
[0027] The following are examples of an application of the present
invention to coating a porous support layer. In both examples, the
porous support layer is fabricated from MA956 oxide dispersed
strengthened alloy obtained from Special Metals Corporation,
Huntington, W.Va., United States.
EXAMPLE 1
[0028] Composite elements consisting of a coating deposited on a
perforated substrate to simulate a composite structure of an ion
transport membrane were fabricated in accordance with prior art
techniques. The substrate was a metallic disc about 30 mm in
diameter and 1.8 mm in thickness. This was perforated to form
straight pores by electron beam drilling. The resultant pores had a
diameter of about 120 microns to produce a porosity of about 15
percent.
[0029] A plasma spray coating was deposited on the substrate that
consisted of a mixed conducting ceramic formed of stronium doped
lanthanum chromium iron oxide ("LSCF"). The particle sizes were
between about 20 microns and about 30 microns agglomerated from
primary particle sizes of between about 0.3 and about 0.5 microns.
The coating consisted of two layers, namely a porous layer such as
layer 18 and a dense gas separation layer such as dense layer 20.
The porous layer 18 was fabricated from LSCF powder blended with 40
percent weight graphite. The thickness of the porous and dense
layers was between about 200 and about 250 microns.
[0030] The composite element was tested in a test reactor using an
85 percent hydrogen/CO.sub.2 mixture on the anode side and air
adjacent the dense layer. The test reactor operated at about
1000.degree. C. Low fluxes of between about 7 and about 8
sccm/cm.sup.2 were observed. It is believed these low fluxes are
the result of the pores becoming plugged.
EXAMPLE 2
[0031] In this example, a porous substrate of a composite structure
was formed in the manner of example 1 and was filled with a
commercially available glue to prevent any coating from entering
the pores. The glue penetrated the pores under the force of
gravity. After about 10 minutes the composite structure was placed
into an oven at a temperature of about 70.degree. C. and for about
30 minutes to dry the glue within the channels to form plugs. The
glue at the surface was then removed by sandblasting at 20 psi
using aluminum oxide sand having a particle size of about 100
microns.
[0032] The substrate was then coated by plasma spraying a two-layer
LSCF coating having dense and porous layers in the manner outlined
in Example 1. After completion of the plasma spraying, the
composite was placed into a closed container with an appropriate
amount of acetone for 60 minutes to remove the glue. The composite
structure was rinsed with fresh acetone and was then dried. The
resultant composite structure was tested at a temperature of about
1000.degree. C. Higher fluxes as compared to Example 1, of between
about 16 and about 18 sccm/cm.sup.2 were detected.
[0033] As will occur to those skilled in the art, numerous
additions, changes and omissions can be made without departing from
the spirit and the scope of the present invention.
* * * * *